Permissibility of gifting to a son for marriage if he is unable

Question: His Eminence the Shaykh / Abdulaziz ibn Abdullah ibn Baz, the Grand Mufti of the Kingdom of Saudi Arabia, may Allah grant him understanding in all good.
Peace be upon you, and Allah's mercy and blessings. As for what follows:
So I ask your Eminence to issue a ruling to me on the following matter:
I heard your Eminence’s fatwa regarding helping sons with marriage, and you saw, may Allah preserve you, that helping them is permissible and does not contradict the text of the hadith: If I have six sons, four of whom have married and I helped them, and the last two remain, and they are young, is it permissible for me to deposit with a trustworthy person their assistance, on the condition that it is not given to each of them except at the time of marriage, and if they do not marry or Allah makes them independent of this assistance, it returns to all their brothers as inheritance?
And upon you be peace, and Allah’s mercy and blessings, after that:
It is not permissible for you to designate the two young ones for something if they are not of marriageable age due to their youth. When they grow up and become eligible for marriage, it is obligatory for you to help them if they are unable, just as you helped their four brothers. And success is from Allah.